The invention relates to a method for dynamically checking weights of objects which are conveyed with a conveying mechanism at an adjustable conveying rate over a weight-sensitive zone of a weighing mechanism, wherein the weight-sensitive zone supplies individual measured weight values at regular intervals, from which resultant weight values are derived through averaging in a digital evaluation unit.
The invention also relates to an apparatus for dynamically checking weights of objects, comprising
a weighing mechanism with a weight-sensitive zone,
a conveying mechanism which conveys the objects at an adjustable conveying rate over the weight-sensitive zone of the weighing mechanism,
wherein the weight-sensitive zone supplies individual measured weight values at regular intervals, from which a digital evaluation unit connected downstream derives a resultant weight value by averaging.
Methods and apparatus of this type are disclosed by DE 103 22 504 A1 and its published US counterpart US 2007/0181349 A1, which is incorporated into the present application by reference. This document discloses “control scales” and a method for the adjustment and operation thereof. Control scales are understood to be weighing mechanisms having a weight-sensitive zone to which objects are conveyed more or less continuously by a conveying mechanism in order to be weighed there. The weighed objects are then transported away by the conveying mechanism and possibly sorted according to the weighing result. A typical field of use of such control scales is the final checking of nominally identical objects. An example thereof is the final filling quantity checking of cans of preserved food.
A fundamental problem of such systems lies in finding a satisfactory compromise between weighing accuracy and weighing speed. Such systems are also typically operated in an industrial environment with severe interfering influences. A typical configuration involves, for example, the conveying of the objects by a fast-moving conveyor belt which passes the objects to a separate conveyor belt zone supported on the weight-sensitive zone of the weighing mechanism, and this conveyor belt zone subsequently passing the objects, following weighing, to a further conveyor belt section. In systems of this type, the weighing signal is overlaid with significant interfering influences firstly from the movement of the conveyor belt, secondly from the only partial contact of the object with the conveyor belt section supported on the weighing mechanism on entry and exit, and thirdly from other vibrations in the industrial environment. It has therefore proved useful, instead of a single measurement value, to record a plurality of individual measurement values for an object and, with the use of suitable averaging, to derive a resultant weight value. In the document cited, averaging is carried out over a particular section of the sequence of individual measurement values. Within the context of a pre-setting procedure wherein a plurality of objects are weighed while varying parameters for the section, the optimum position and length of the averaging section is found by “automatic” experimentation. This section selection is then maintained for the subsequent checking operation of the system.